1. Field of the Invention
The present invention relates to a wiper apparatus for making a wiper blade of a vehicle or the like perform reciprocating wiping operation by normal and reverse rotation of a motor, and in particular to a technique effectively applied to a wiper apparatus suitable for control of a rise-up wiper of a direct drive system.
2. Related Art Statement
For example, among techniques studied by the inventor, there exists a link-type rear wiper for a vehicle, in which a rack-and-pinion mechanism or link mechanism interlocked with a wiper blade is driven by using a worm wheel interlocked with normal and reverse rotation of a motor. This link-type is classified into an outside link-type in which these mechanism are arranged outside the motor, and an inside link-type in which these mechanism are arranged integrally with a reduction gear. Further, there has been used a direct drive system in which a relay plate is driven being interlocked with rotation of a worm wheel, and a wiper blade is made to perform reciprocating wiping operation according to relative position between this relay plate and contacts.
Among these techniques, the direct drive system has many advantages in making a wiper apparatus smaller and lighter, and in installation in narrow space, and, in particular, suitably used for a rear wiper etc. In the rear wiper, there has been used a rise-up type in which, when a wiper blade is stopped, it is further driven from a turning position to a storing position so as not to be obstruction for opening a rear glass hatch.
As a rise-up-wiper of this direct drive system, it is possible to consider a following technique. Namely, in such structure that a worm wheel is rotated being interlocked with rotation of a motor and a boss interlocked with the rotation of the worm wheel makes a relay plate rotate, a wiper blade performs reciprocating wiping operation by normal and reverse rotation of the motor. In that case, after detecting signal change from the relay plate of the motor, a relay within a controller connected to this relay plate is switched so that electric braking is applied to the motor.
As a rise-up wiper of such a direct drive system, may be referred to a technique described in Japanese Un-examined Patent Laid-Open No. 3-67754, for example. This technique may be briefly described as follows. Namely, there is provided a relay plate interlocked with rotation of a motor which can normally and reversely rotate and the relay plate has switching positions of storing, lower turning, and upper turning. Based on these positions of storing, lower turning, and upper turning, rotational direction of the motor can be switched.
In such a rise-up wiper of the direct drive system, there arise a delay of time between detection of the switching position and starting of braking. Accordingly, there exists such a problem that the turning position tends to be changed owing to variation in load by glass surface on which the wiper blade performs reciprocating wiping operation.
Further, when the relay is switched based on the change of the signal from the relay plate, noise may be added to input signal at the turning positions. In that case, the relay, which is operated based on this input signal, is caused to chatter and the motor may continue rotating in the normal direction so that the wiper blade abuts against a pillar.
Further, in the technique described in the above-described Japanese Un-examined Patent Laid-Open No. 3-67754, the rotational direction of the motor is switched directly based on a position of the relay plate. Accordingly, there may arise such a problem that, when a wiper switch is turned OFF immediately after being turned ON, a contact contacting with the relay plate is not switched, so that the wiper blade is stopped on the spot.
Further, when the rotational direction of the motor is switched, twice voltage as much as ordinary one, i.e. power-supply voltage to grounding voltage and the grounding voltage to the power-supply voltage, are directly applied to the contact itself which contacts with the relay plate. And the motor is switched at once from the normal direction to the reverse direction of rotation, and from reverse direction to the normal direction. Accordingly, unnecessarily large load may be applied to the motor.
Thus, an object of the present invention is to provide a wiper apparatus in which switching of contacts and a motor does not cause unnecessary large load, and electric braking is performed directly by relay plate interlocked with driving of the motor, without using a procedure for relay switching. By this, it is possible to remove the delay until starting braking and to increase accuracy of the turning positions, as well as to prevent malfunction of the wiper blade.
The above-described and other objects and new features of the present invention will be made obvious from the following description and the attached drawings.